Construction Machine, Hybrid Hydraulic Excavator, And Output Torque Control Method For Motor Generator

ABSTRACT

A construction machine includes a swing speed detection unit that detects an actual swing speed of an upper structure, a lever command speed calculation unit that calculates a lever command speed based on an operation amount of a swing lever for swinging the upper structure, a torque command value calculation unit that calculates a torque command value based on a command speed based on the calculated lever command speed, a command value output unit that outputs a command torque to a rotary motor generator based on the torque command value calculated by the torque command value calculation unit and the swing speed detected by the swing speed detection unit, and a command value output restriction unit that restricts the output of the torque command value from the command value output unit under predetermined conditions.

TECHNICAL FIELD

The present invention relates to a construction machine, a hybrid hydraulic excavator, and an output torque control method for a motor generator.

BACKGROUND ART

A hybrid electric rotary excavator including a motor generator for driving an upper structure and a hydraulic actuator for driving other working equipment and a carrier has been known (see, for instance, Patent Literature 1).

Since the electric rotary excavator uses the motor generator in order to swing the upper structure, the motion of the upper structure is not affected by a lift operation of a boom and/or an arm even when the upper structure is swung simultaneously with the lift operation of the hydraulically driven boom and arm. Accordingly, an energy loss in a control valve and the like can be reduced as compared to an instance in which the upper structure is hydraulically driven, so that energy efficiency can be improved.

When the swing speed of such an electric rotary excavator is to be controlled, a lever command speed is calculated based on a lever signal of a swing lever. Then, the lever command speed is compared with an actual speed to obtain a deviation, and a torque command value is calculated based on the deviation to accelerate and decelerate the swing motion of the electric rotary excavator using a torque output corresponding to the torque command value.

Specifically, a jerk command speed for providing the most appropriate acceleration (jerk value) for the lever command speed is calculated based on the lever signal of the swing lever. Then, a feed-forward torque command value that reduces a constant speed deviation of the swing speed with respect to the calculated jerk command speed is calculated to control the swing speed (see, for instance, Patent Literature 2).

CITATION LIST Patent Literature(s)

Patent Literature 1 WO 2005/111322

Patent Literature 2 WO 2006/054581

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

The electric rotary excavator occasionally performs excavation work while a bucket is lateral-pressed to an excavation wall. In such a case, it is necessary to operate the boom, the arm and/or the bucket while the swing lever is operated.

At this time, though the swing lever is operated by an operator, the upper structure itself receives a reaction force from the excavation wall, so that the swing speed is kept at substantially zero.

When the operator sets the swing lever in neutral in this state, since the reaction force is larger than an output torque of a swing motor, the upper structure is pushed back toward a side opposite the excavation wall, thereby causing vibrations before the upper structure stops.

An object of the invention is to provide a construction machine, a hybrid hydraulic excavator and an output torque control method for a motor generator capable of restraining vibrations when the swing motion is stopped while a lateral-press excavation in which a swing operation and a working equipment operation are simultaneously conducted is performed.

Means for Solving the Problem(s)

A construction machine according to an aspect of the invention includes:

an undercarriage;

an upper structure swingably provided to the undercarriage and driven by a motor generator;

working equipment provided to the upper structure;

a rotation speed detection unit configured to detect an actual swing speed of the upper structure;

a lever command speed calculation unit configured to calculate a lever command speed based on an operation amount of a swing lever configured to swing the upper structure;

a torque command value calculation unit that calculates a torque command value based on a command speed based on the calculated lever command speed;

a command value output unit configured to output the torque command value to the motor generator based on the torque command value calculated by the torque command value calculation unit and the swing speed detected by the rotation speed detection unit; and

a command value output restriction unit configured to restrict the output of the torque command value from the command value output unit when: the actual rotation speed detected by the rotary speed detection unit is smaller than a first threshold; a deviation between the lever command speed calculated by the lever command speed calculation unit and the actual swing speed detected by the rotation speed detection unit is greater than a second threshold; and the lever command speed calculated by the lever command speed calculation unit is smaller than a predetermined value.

According to the above aspect of the invention, when the actual swing speed of the upper structure is smaller than the first threshold and the deviation between the lever command speed and the actual swing speed is greater than the second threshold, the upper structure is not swung irrespective of the operation on the swing lever, and thus it can be judged that the construction machine is in the lateral-press excavation work. Then, when it is found that the lever command speed is smaller than the predetermined value, it can be judged that an operator stops the lateral-press excavation work. At this time, since the command value output restriction unit restricts the output of the torque command value from the command value output unit, the command value output unit is kept from outputting a torque command value in the same direction as a direction of a reaction force applied to the working equipment, so that the generation of vibrations on the upper structure can be prevented.

A hybrid hydraulic excavator according to another aspect of the invention includes:

an undercarriage;

an upper structure swingably provided to the undercarriage and driven by the motor generator; and

working equipment provided to the upper structure, the working equipment comprising a boom swingably provided to the upper structure, an arm swingably provided to the boom, and a bucket swingably provided to the arm, where

an electric power is transferred between the motor generator and a rechargeable battery or a generator motor, and

the boom, the arm, and the bucket are hydraulically driven. The hybrid hydraulic excavator further includes:

a rotation speed detection unit configured to detect an actual swing speed of the upper structure;

a lever command speed calculation unit configured to calculate a lever command speed based on an operation amount of a swing lever configured to swing the upper structure;

a torque command value calculation unit that calculates a torque command value based on a command speed based on the calculated lever command speed;

a command value output unit configured to output the torque command value to the motor generator based on the torque command value calculated by the torque command value calculation unit and the swing speed detected by the rotation speed detection unit; and

a command value output restriction unit configured to restrict the output of the torque command value from the command value output unit when: the actual rotation speed detected by the rotary speed detection unit is smaller than a first threshold; a deviation between the lever command speed calculated by the lever command speed calculation unit and the actual swing speed detected by the rotation speed detection unit is greater than a second threshold; and the lever command speed calculated by the lever command speed calculation unit is smaller than a predetermined value.

According to this aspect of the invention, the same effect(s) and advantage(s) as those of the above aspect of the invention can be obtained.

An output torque control method for a motor generator according to still another aspect of the invention is performed in a construction machine including: an undercarriage; an upper structure swingably provided to the undercarriage and driven by a motor generator; working equipment provided to the upper structure; and a controller. The method includes steps below performed by the controller of the construction machine:

detecting an actual swing speed of the upper structure;

calculating a lever command speed based on an operation amount of a swing lever configured to swing the upper structure;

calculating a torque command value based on the calculated lever command speed;

outputting the torque command value to the motor generator based on the calculated torque command value and the detected actual swing speed of the upper structure; and

restricting the output of the torque command value to the motor generator when:

the detected actual swing speed is smaller than a first threshold;

a deviation between the calculated lever command speed and the detected actual swing speed is greater than a second threshold; and

the calculated lever command speed is zero.

According to this aspect of the invention, the same effect(s) and advantage(s) as those of the above aspect of the invention can be obtained.

BRIEF DESCRIPTION OF DRAWING(S)

FIG. 1 is a perspective view showing a structure of a construction machine according to an exemplary embodiment of the invention.

FIG. 2 is a block diagram showing a structure of a drive system of the construction machine according to the exemplary embodiment.

FIG. 3 is a functional block diagram of a swing controller according to the exemplary embodiment.

FIG. 4 is a graph for explaining a jerk command speed calculation unit of the exemplary embodiment.

FIG. 5 is a flow chart for explaining a function of the exemplary embodiment.

FIG. 6 is a perspective view for explaining an effect of the exemplary embodiment.

FIG. 7 is a graph for explaining the effect of the exemplary embodiment.

DESCRIPTION OF EMBODIMENT(S)

Exemplary embodiment(s) of the invention will be described below with reference to the attached drawings.

[1] Overall Arrangement

FIG. 1 shows a working machine according to the exemplary embodiment in a form of a hybrid electric rotary excavator 1. The electric rotary excavator 1 includes an undercarriage 2, an upper structure 3 and working equipment 5.

Though not illustrated, the undercarriage 2 includes a truck frame and a pair of travel devices 2A (sometimes collectively referred to as a travel device 2A hereinafter) provided on both ends of the truck frame in a vehicle-width direction orthogonal to a travel direction. Each of the travel devices 2A includes a drive wheel and an idler wheel provided to the truck frame, and a crawler 2B wrapped around the drive wheel and the idler wheel. The travel device 2A moves the electric rotary excavator 1 forward and backward by driving the drive wheel in an extension direction of the crawler 2B.

The upper structure 3 is swingably provided on the truck frame of the undercarriage 2 via a swing circle. The upper structure 3 is driven by a motor generator (detailed later).

A cab 4 is provided at a front left side of the upper structure 3 in the travel direction. The working equipment 5 is provided at a front center of the upper structure 3 in a manner adjacent to the cab 4. A counterweight 3A is provided to a rear side of the upper structure 3 (i.e. a side opposite the cab 4 and the working equipment 5). The counterweight 3A is provided to keep a weight balance during the excavation work of the electric rotary excavator 1.

An operator gets in the cab 4 to handle the electric rotary excavator 1. Though not illustrated in FIG. 1, an operator's seat is provided in the cab 4. Control levers are provided on both sides of the operator's seat. Travel pedal(s) are provided on the floor surface of the cab 4.

The working equipment 5 includes a boom 6, an arm 7, a bucket 8, and cylinders including a boom cylinder 6A, an arm cylinder 7A, and a bucket cylinder 8A respectively for moving the boom 6, the arm 7 and the bucket 8.

A base end of the boom 6 is movably connected to the upper structure 3. The boom cylinder 6A having ends respectively connected to the upper structure 3 and the boom 6 is configured to be extended and retracted to vertically move the boom 6.

The arm 7 has a base end swingably connected to a distal end of the boom 6, so that the arm 7 can be vertically moved by an extension and retraction of the arm cylinder 7A having ends respectively connected to the boom 6 and the arm 7.

The bucket 8 has a base end swingably connected to a distal end of the arm 7, so that the bucket 8 can be moved by an extension and retraction of the bucket cylinder 8A having ends respectively connected to the arm 7 and the bucket 8.

The boom cylinder 6A, the arm cylinder 7A, and the bucket cylinder 8A are hydraulic cylinders driven by hydraulic oil discharged by a hydraulic pump.

It should be noted that, though the upper structure 3 is driven by the motor generator in the exemplary embodiment, the scope of the invention is not limited thereto. Specifically, the electric rotary excavator 1 may alternatively be a hybrid or electrically driven electric rotary excavator in which at least one of the boom 6, the arm 7, the bucket 8 and the undercarriage 2 is driven by the motor generator.

FIG. 2 shows an overall arrangement of a drive system of the electric rotary excavator 1. It should be noted that a swing center of the upper structure 3 is defined as an origin, the travel direction of the undercarriage 2 is referred to as a front-back direction and a direction orthogonal to the travel direction is referred to as a right-left direction in the description hereinbelow.

The electric rotary excavator 1 includes an engine 11 (drive source), a generator motor 13 driven by the engine 11 to generate electric power, a rechargeable battery 17 configured to store the electric power, inverters 13I, 171, a transformer 17C, a hydraulic pump 12, control levers 20L, 20R, a hydraulic control valve 14, an engine controller 11A, a pump controller 14A, a hybrid controller 16 and a multimonitor 23. The electric power generated by the generator motor 13 and/or the electric power discharged by the rechargeable battery 17 is supplied to a rotary motor generator 19 to drive the rotary motor generator 19 to cause a swing motion of the upper structure 3.

The engine 11 is driven by a control command from the engine controller 11A to drive the hydraulic pump 12 and the generator motor 13.

The hydraulic drive system includes the hydraulic control valve 14, the above-described boom cylinder 6A, the arm cylinder 7A, the bucket cylinder 8A, and a travel motor 15, which are driven by the hydraulic pump 12 (hydraulic source). The hydraulic control valve 14 is driven by a pilot hydraulic pressure (PPC pressure) generated by operating the control levers 20L, 20R. The hydraulic pump 12 is a variable displacement pump having a variable displacement unit (e.g. a swash plate and an axle). The hydraulic pump 12 includes a swash-plate-angle detection sensor for detecting a swash plate angle of the hydraulic pump 12. The detected swash plate angle is inputted to the pump controller 14A and the pump controller 14A issues a control command to variably control an output flow of the hydraulic pump 12.

A motor drive system includes the generator motor 13, the hybrid controller 16, the rechargeable battery 17, the rotary motor generator 19, the inverters 13I, 19I, and the transformer 17C.

The hybrid controller 16 includes an input unit, an output unit, a calculation unit, and a storage.

The input unit of the hybrid controller 16 receives a swing operation command of the upper structure 3, and information acquired by a sensor provided mainly to the motor drive system (e.g. a position information of the rotary motor generator 19 and voltage between systems connected with the inverters 13I, 19I and the transformer 17C).

The output unit of the hybrid controller 16 issues a command to the inverters 13I, 19I and the transformer 17C. The inverters 13I, 19I and the transformer 17C are connected with each other via power lines. In response to the command from the hybrid controller 16, the electric power is transferred between the inverter 13I and the generator motor 13, between the inverter 19I and the rotary motor generator 19, and between the transformer 17C and the rechargeable battery 17.

The calculation unit of the hybrid controller 16 calculates a rotation speed of the rotary motor generator 19 and a drive command for the rotary motor generator 19 (described later).

The storage of the hybrid controller 16 stores drive characteristics of the rotary motor generator 19.

The rotary motor generator 19 is driven by the power from the generator motor 13 and/or the rechargeable battery 17. The rotary motor generator 19 converts a braking force into the electric power when the upper structure 3 is braked and supplies the electric power to the generator motor 13 and the rechargeable battery 17.

The rotary motor generator 19 includes a sensor 24 (e.g. a resolver), which detects a rotary position of the rotary motor generator 19 and outputs the detected rotary position to the hybrid controller 16. It should be noted that the electric power to the rotary motor generator 19 is calculated using a voltage between the systems and the electric current or the rotation speed of the rotary motor generator 19.

These drive systems are configured to be driven in response to an operator's operation on a left control lever 20L and a right control lever 20R provided in the cab 4.

Specifically, the boom 6 is configured to be moved upward or downward when the operator operates the right control lever 20R in the front-back direction. The bucket 8 is configured to conduct the excavation/damping operation when the operator operates the right control lever 20R in the right-left direction. The arm 7 is configured to conduct the damping/excavation operation when the operator operates the left control lever 20L in the front-back direction. The upper structure 3 is configured to be swung in the right-left direction when the operator operates the left control lever 20L in the right-left direction.

When the left control lever 20L is operated in the right-left direction in order to swing the upper structure 3, the PPC command detected by the PPC pressure detection unit 21 is received by the pump controller 14A and the hybrid controller 16.

The hybrid controller 16 outputs a swing command to the inverter 19I. The inverter 19I supplies the electric power to the rotary motor generator 19 to drive the rotary motor generator 19.

Further, in response to the operation on the control levers 20L, 20R, the PPC pressure is directly inputted to the hydraulic control valve 14 to control the hydraulic oil from the hydraulic pump 12 to drive the cylinders 6A, 7A, 8A, and the travel motor 15.

A throttle dial 22 and the multimonitor 23 are provided in the cab 4 on the upper structure 3.

A control command to the engine controller 11A is issued by operating the throttle dial 22 to control the output of the engine 11.

The multimonitor 23 includes a control unit 23A and a display 23B. The multimonitor 23 may be a touch panel configured to be operated by a direct touch on the display.

The control unit 23A includes a plurality of operation buttons independent of the monitor and is configured to switch the display status and input an operation command.

The status of the engine 11 (e.g. a residual fuel amount and cooling water temperature) as well as temperature conditions and the like of the generator motor 13, the rechargeable battery 17 and the rotary motor generator 19 is displayed on the display 23B.

[2] Arrangement of Calculation Unit 18 of Hybrid Controller 16

FIG. 3 shows a functional block diagram of a calculation unit 18 of the hybrid controller 16 according to the exemplary embodiment of the invention. The calculation unit 18 of the hybrid controller 16 includes a lever command speed calculation unit 31, a jerk command speed calculation unit 32, a reaction-force control command speed calculation unit 33, a torque command value calculation unit 34, a command value output unit 35, and a command value output restriction unit 36.

Further, the hybrid controller 16 is connected with a rotary speed detection unit 37 configured to detect the swing speed of the upper structure 3 driven by the rotary motor generator 19, a rotary position detection unit 38 configured to detect the rotary position of the rotary motor generator 19, and an output torque detection unit 39 configured to detect an output torque of the rotary motor generator 19, so that an actual swing speed and an actual rotary position of the upper structure 3, and a detection value of the output torque of the rotary motor generator 19 are fed back to the hybrid controller 16. The swing speed to be detected by the rotary speed detection unit 37 and the rotary position of the rotary motor generator 19 to be detected by the rotary position detection unit 38 are obtained based on the detection value of the above-described sensor 24 (see FIG. 2). The output torque of the rotary motor generator 19 is obtained based on the above-described voltage between the systems, and the rotation speed of the rotary motor generator 19 or the electric current inputted to the rotary motor generator 19. It should be noted that, in the description below, the operation on the left control lever 20L in the right-left direction for operating the upper structure 3 will be referred to as the operation on the “swing lever 20L.”

The lever command speed calculation unit 31 calculates the lever command speed based on a lever operation amount of the swing lever 20L detected by the PPC pressure detection unit 21. The lever command speed calculation unit 31 includes a table in which the lever operation amount is associated with the lever command speed, and calculates and outputs the lever command speed with reference to the table.

The jerk command speed calculation unit 32 calculates a jerk command speed including a gradient of the acceleration or deceleration of the upper structure 3 based on the lever command speed calculated by the lever command speed calculation unit 31. Specifically, as shown in FIG. 4, the jerk command speed calculation unit 32 receives a lever command speed Vi of the swing lever 20L during an acceleration period (receives a lever operation command changed from Vi to 0 during a deceleration period), and calculates the acceleration (deceleration) G so that a constant jerk value Ja can be obtained until the acceleration reaches a predetermined acceleration Ga (or the deceleration G reaches deceleration Gb during the deceleration period). In order to avoid sharp acceleration (deceleration) of the upper structure 3 when the lever command speed Vi is inputted (when the lever command speed input is changed from Vi to 0 during the deceleration period), the acceleration Ga (deceleration Gb during the deceleration period) is calculated based on the jerk value Ja in a form of the gradient of the acceleration (a jerk value Jb in a form of the gradient of the deceleration during the deceleration period) and a jerk command speed Vo is calculated and outputted in order to perform a smooth acceleration (deceleration). It should be noted that, when the upper structure 3 is in a low-speed state where the swing speed is at a first threshold (described later) or less, the jerk command speed calculation unit 32 exceptionally outputs the lever command speed as the jerk command speed in a section where the lever command speed is changed from Vi to 0. Then, the above exceptional process is cleared when the swing speed falls below the first threshold (i.e. immediately before the swing motion is stopped).

The reaction-force control command speed calculation unit 33 calculates a reaction-force control command speed for controlling the position of the upper structure 3 with reference to the current position (origin) of the rotary motor generator 19. Specifically, the reaction-force control command speed calculation unit 33 calculates the origin position of the rotary motor generator 19 based on the current position of the rotary motor generator 19 detected by the rotary position detection unit 38, the actual swing speed detected by the rotary speed detection unit 37, the output torque of the rotary motor generator 19 detected by the output torque detection unit 39, the calculated lever command speed, and the jerk command speed.

When the upper structure 3 is actually swung in a direction different from the direction indicated by the lever operation command of the swing lever 20L, the reaction-force control command speed calculation unit 33 calculates the reaction-force control command speed by applying a gain to a difference between the origin position and the current position of the rotary motor generator 19. The calculated reaction-force control command speed is a command speed at which a lock torque for locking the position of the upper structure 3 is applied so that the rotary motor generator 19 is not reversely rotated in spite of an external force applied while the upper structure 3 is stopped or the lever command speed.

The torque command value calculation unit 34 calculates a feed-forward torque command value (referred to as an FF torque command value hereinafter) based on the acceleration G calculated by the jerk command speed calculation unit 32 and a predetermined inertial value. It should be noted that the torque command value calculation unit 34 calculates the FF torque command value to be zero when the output of the torque command value is restricted by the command value output restriction unit 36 as described later.

The command value output unit 35 outputs the torque command value calculated by the torque command value calculation unit 34 to the rotary motor generator 19. Specifically, the command value output unit 35 adds the calculated jerk command speed to the reaction-force control command speed to set a command speed, and subtracts the actual swing speed detected by the rotary speed detection unit 37 from the command speed to define a difference. Then, the command value output unit 35 applies a torque conversion to the difference to define a speed deviation torque command value.

Subsequently, the command value output unit 35 adds the torque-converted speed deviation torque command value to the FF torque command value calculated by the torque command value calculation unit 34 to calculate the torque command value and outputs the torque command value to the rotary motor generator 19.

The command value output restriction unit 36 restricts an output of the torque command value from the command value output unit 35 under predetermined conditions.

The output of the torque command value is restricted by the command value output restriction unit 36 when all of the following conditions are satisfied.

Condition 1: The actual swing speed detected by the rotary speed detection unit 37 is smaller than a first threshold.

Condition 2: The operator sets the swing lever 20L at a neutral position when the inclination angle of the swing lever 20L is smaller than a predetermined angle and is trying to stop the swing motion of the upper structure 3.

Condition 3: The jerk command speed calculated by the jerk command speed calculation unit 32 is smaller than a third threshold.

Condition 4: A deviation between the command speed obtained by adding the reaction-force control command speed to the calculated jerk command speed and the actual swing speed is larger than a second threshold (i.e. an excavation work is performed while an external force is applied on the bucket 8 in the swing direction).

In the exemplary embodiment, the second threshold is defined as a rotation speed larger than the rotation speed defined as the first threshold, and the third threshold is defined as a rotation speed larger than the rotation speed defined as the second threshold.

The following judgment is made according to the above-described conditions. With the use of the conditions 1 and 2 as part of the judgment conditions, it can be judged that the swing speed of the upper structure is low and the operator hopes to stop the swing motion. With the use of the condition 3 as one of the judgment conditions, it can be judged that the jerk command speed is low and the swing speed is low. With the use of the condition 4 as one of the judgment conditions, it can be judged that the swing command speed is different from the actual swing speed due to an external force.

Using the above conditions 1 to 4 for restricting the output of the FF torque command, unintentional output of the FF torque generated when the speed of the swing motion is low and the reaction force is applied and the upper structure is moved in an unintended direction can be avoided. It should be noted that the above condition 3 in the above conditions is not requisite.

Further, the command value output restriction unit 36 sets the FF torque command value at zero to restrict the output of the torque command value from the command value output unit 35 also when the reaction-force control command speed calculated by the reaction-force control command speed calculation unit 33 is smaller than the jerk command speed calculated by the jerk command speed calculation unit 32.

On the other hand, the command value output restriction unit 36 does not set the FF torque command value at zero when the following conditions are satisfied.

Condition 5: The external force is not applied on the bucket 8 and the actual swing speed is not greatly different from the jerk command speed.

Condition 6: The speed deviation torque obtained based on the deviation between the command speed and the actual swing speed is in the same direction as the FF torque command value (the absolute value of the actual swing speed>the absolute value of the jerk command speed).

When the above conditions are satisfied, the command value output restriction unit 36 does not set the FF torque command value at zero but directly outputs the calculated FF torque command value to the command value output unit 35 even if the conditions 1 to 3 are satisfied.

[3] Effects of Embodiment (Output Torque Control Method for Motor Generator)

Next, effects of the exemplary embodiment will be described below with reference to a flowchart shown in FIG. 5.

Initially, the PPC pressure detection unit 21 detects the operation amount of the swing lever 20L (step S1), and outputs the detected lever operation amount to the lever command speed calculation unit 31.

The lever command speed calculation unit 31 calculates the lever command speed based on the lever operation amount (step S2), and outputs the lever command speed to the jerk command speed calculation unit 32.

The jerk command speed calculation unit 32 calculates the jerk command speed based on the calculated lever command speed (step S3).

The torque command value calculation unit 34 calculates the FF torque command value based on the acceleration G calculated based on the jerk command speed, and the inertial value (step S4).

The reaction-force control command speed calculation unit 33 calculates the origin position of the rotary motor generator 19 and the difference between the origin position and the actual swing position, and applies a gain and integration to the difference to calculate the reaction force command speed (step S5).

The command value output restriction unit 36 judges whether the actual swing speed (above-described condition 1) is smaller than the first threshold (step S6).

When the condition 1 is satisfied (Yes in step S6), the command value output restriction unit 36 judges whether or not the lever command speed is zero (second condition) to determine whether or not the operator is trying to stop the swing motion of the upper structure 3 (step S7).

When the second condition is satisfied (Yes in step S7), the command value output restriction unit 36 judges whether the jerk command speed is at or less than the third threshold (the third condition) (step S8).

When the third condition is satisfied (Yes in step S8), the command value output restriction unit 36 judges whether or not the command value obtained by adding the reaction-force control command speed to the jerk command speed is greater than the second threshold (the fourth condition) (step S9). When the fourth condition is satisfied (Yes in step S9), the command value output restriction unit 36 sets the FF torque command value at zero and outputs the FF torque command value to the command value output unit 35 (step S11).

On the other hand, when one of the first to fourth conditions (S6 to S9) is not satisfied (S6 to S9: No), the command value output restriction unit 36 judges whether or not the reaction-force control command speed is greater than the jerk command speed (step S10). When the reaction-force control command speed is not greater than the jerk command speed (step S10: No), the torque command value calculation unit 34 outputs the FF torque determined based on the acceleration G and the inertial value to the command value output unit 35 (step S12).

When the command value output restriction unit 36 judges that the reaction-force control command speed is greater than the jerk command speed (Yes in step S10), the torque command value calculation unit 34 sets the FF torque command value at zero and outputs the FF torque command value to the command value output unit 35 (step S11).

The command value output unit 35 adds the speed deviation torque command value to the FF torque command value to define the torque command value and outputs the torque command value to the rotary motor generator 19 (step S13).

[4] Advantage(s) of Exemplary Embodiment(s)

The exemplary embodiment offers the following advantages.

It is assumed that an excavation work is performed while a left side of the bucket 8 is in contact with an excavation wall W as shown in FIG. 6. The operator handles a bucket control lever to downwardly apply an excavation force F1 and simultaneously handles the swing lever 20L leftward. In this state, since a reaction force F2 from the excavation wall W acts on the bucket 8, the actual swing speed of the upper structure 3 is substantially zero irrespective of the constant output of the jerk command speed.

When the operator sets the swing lever 20L to a neutral position at a time t1 (see FIG. 7), the leftward jerk command speed is reduced until the jerk command speed immediately before the swing motion is stopped is commanded based on the lever command speed. At the jerk command speed immediately before the swing motion is stopped, since the reaction force F2 from the excavation wall W exceeds the output torque of the rotary motor generator 19, the upper structure 3 swings rightward. At this time, since the FF torque command value F3 is outputted to cause a rightward swing motion, a large torque fluctuation occurs to cause vibrations on the rotary motor generator 19. The subsequent reaction-force control command speed enlarges the speed deviation torque, which is balanced with the reaction force F2, thereby stopping the upper structure 3.

The above is observable in a graph shown in FIG. 7. It should be noted that the upper side of an ordinate axis of the graph indicates a left side in the swing direction in FIG. 6 and the lower side indicates a right side in the swing direction in FIG. 6. When the operator operates the swing lever 20L to press the bucket 8 onto the excavation wall W and then sets the swing lever 20L to the neutral position, since the actual swing speed is low, the jerk command speed decreases in conformity with the lever command speed until a time immediately before the swing motion is stopped and slowly comes close to zero based on the jerk command speed from the time immediately before the swing motion is stopped.

A description is made on a comparative example having no command value output restriction unit 36 (i.e. an instance before no countermeasures are taken). The actual swing speed of the upper structure 3 does not increase while the working equipment 5 is pressed onto the excavation wall W by an operation of the swing lever 20L, since the output torque of the rotary motor generator 19 is balanced with the reaction force F2. When the operator sets the swing lever 20L to the neutral position at the time t1, the upper structure 3 is swung in a direction (a minus direction) opposite the direction in which the working equipment 5 is pressed onto the excavation wall W due to the reaction force F2 from the excavation wall W.

At this time, the output torque outputted by the command value output unit 35 rapidly decreases when the swing lever 20L is set to the neutral position. This is because the speed deviation torque rapidly decreases in conjunction with the decrease in the jerk command speed and the rightward FF torque is outputted. When the FF torque command value F3 is outputted, the torque command value is outputted to the rotary motor generator 19 in a direction promoting the rapid decrease in the output torque outputted by the command value output unit 35 to promote the rightward swing motion. Subsequently, in accordance with the enhancement of the reaction force control, the output torque outputted by the command value output unit 35 is outputted leftward to keep the position of the working equipment at a time t2 to stop the working equipment.

In contrast, in the arrangement modified according to the exemplary embodiment (i.e. an instance after the countermeasures are taken), since the FF torque command value is set at zero and the FF torque command value is not outputted from the command value output unit 35 when all the above-described conditions starting from the condition 1 are satisfied as shown in dashed lines in FIG. 7, the reduction in the output torque of the rotary motor generator 19 can be restrained, so that the change in the actual swing speed of the upper structure 3 can be restrained and the vibrations are reduced.

Further, since the FF torque command value is set at zero when the reaction-force control command speed exceeds the jerk command speed, priority is given to the torque command value based on the reaction-force control command speed, so that the upper structure 3 can be rapidly stopped by the torque command value in a direction resisting the reaction force F2.

[5] Modification(s) of Embodiment(s)

It should be understood that the scope of the invention is not limited to the above-described exemplary embodiment(s), but includes modifications as described below.

In the above-described exemplary embodiment, the reaction-force control command speed calculation unit 33 is provided and the command value output restriction unit 36 restricts the FF torque command value when the reaction-force control command speed calculated by the reaction-force control command speed calculation unit 33 is greater than the jerk command speed calculated by the jerk command speed calculation unit 32. However, the scope of the invention is not limited to the above arrangement but the magnitudes of the reaction-force control command speed and the jerk command speed are not necessarily compared.

The FF torque command value is calculated based on the acceleration calculated by the jerk command speed calculation unit 32 in the above-described exemplary embodiment. However, the scope of the invention is not limited to the above arrangement but the FF torque command value may alternatively be calculated by calculating the acceleration using other methods.

The specific structure and shape in implementing the invention may be altered in a different manner as long as such an alteration is compatible with an object of the invention (e.g. the upper structure is driven using a motor generator and a hydraulic drive mechanism).

EXPLANATION OF CODE(S)

1 . . . electric rotary excavator, 2 . . . undercarriage, 2A . . . travel device, 2B . . . crawler, 3 . . . upper structure, 4 . . . cab, 5 . . . working equipment, 6 . . . boom, 6A . . . boom cylinder, 7 . . . arm, 7A . . . arm cylinder, 8 . . . bucket, 8A . . . bucket cylinder, 11 . . . engine, 11A . . . engine controller, 12 . . . hydraulic pump, 13 . . . generator motor, 13I . . . inverter, 14 . . . hydraulic control valve, 14A . . . pump controller, 15 . . . travel motor, 16 . . . hybrid controller, 17 . . . rechargeable battery, 17C . . . transformer, 18 . . . calculation unit, 19 . . . rotary motor generator, 19I . . . inverter, 20L . . . swing lever, 20R . . . right control lever, 21 . . . PPC pressure detection unit, 22 . . . throttle dial, 23 . . . multimonitor, 23A . . . control unit, 23B . . . display, 24 . . . sensor, 31 . . . lever command speed calculation unit, 32 . . . jerk command speed calculation unit, 33 . . . reaction-force control command speed calculation unit, 34 . . . torque command value calculation unit, 35 . . . command value output unit, 36 . . . command value output restriction unit, 37 . . . swing speed detection unit, 38 . . . rotary position detection unit, 39 . . . output torque detection unit, 3A . . . counterweight, W . . . excavation wall. 

1. A construction machine comprising: an undercarriage; an upper structure swingably provided to the undercarriage and driven by a motor generator; working equipment provided to the upper structure; a swing speed detection unit configured to detect an actual swing speed of the upper structure; a lever command speed calculation unit configured to calculate a lever command speed based on an operation amount of a swing lever configured to swing the upper structure; a torque command value calculation unit configured to calculate a torque command value based on a command speed based on the calculated lever command speed; a command value output unit configured to output the torque command value to the motor generator based on the torque command value calculated by the torque command value calculation unit and the swing speed detected by the swing speed detection unit; and a command value output restriction unit configured to restrict the output of the torque command value from the command value output unit when: the actual rotation speed detected by the rotary speed detection unit is smaller than a first threshold; a deviation between the lever command speed calculated by the lever command speed calculation unit and the actual swing speed detected by the swing speed detection unit is greater than a second threshold; and the lever command speed calculated by the lever command speed calculation unit is smaller than a predetermined value.
 2. The construction machine according to claim 1, wherein the command value output restriction unit is configured to restrict the output of the torque command value when the lever command speed calculated by the lever command speed calculation unit is zero.
 3. The construction machine according to claim 1, further comprising: a jerk command speed calculation unit configured to calculate a jerk command speed including a gradient for an acceleration or deceleration of the upper structure based on the lever command speed calculated by the lever command speed calculation unit, wherein the command value output restriction unit restricts the output of the torque command value from the command value output unit when the jerk command speed calculated by the jerk command speed calculation unit is smaller than a third threshold.
 4. The construction machine according to claim 3, further comprising: a reaction-force control command speed calculation unit configured to calculate a reaction-force control command speed usable for a position control of the upper structure with reference to a current position of the motor generator, wherein the command value output restriction unit restricts the output of the torque command value from the command value output restriction unit when the reaction-force control command speed calculated by the reaction-force control command speed calculation unit is smaller than the jerk command speed calculated by the jerk command speed calculation unit.
 5. A hybrid hydraulic excavator comprising: an undercarriage; an upper structure swingably provided to the undercarriage and driven by a motor generator; and working equipment provided to the upper structure, the working equipment comprising a boom swingably provided to the upper structure, an arm swingably provided to the boom, and a bucket swingably provided to the arm, wherein an electric power is transferred between the motor generator and a rechargeable battery or a generator motor, and the boom, the arm, and the bucket are hydraulically driven, the hybrid hydraulic excavator further comprising: a swing speed detection unit configured to detect an actual swing speed of the upper structure; a lever command speed calculation unit configured to calculate a lever command speed based on an operation amount of a swing lever configured to swing the upper structure; a torque command value calculation unit configured to calculate a torque command value based on a command speed based on the calculated lever command speed; a command value output unit configured to output the torque command value to the motor generator based on the torque command value calculated by the torque command value calculation unit and the swing speed detected by the swing speed detection unit; and a command value output restriction unit configured to restrict the output of the torque command value from the command value output unit when: the actual rotation speed detected by the rotary speed detection unit is smaller than a first threshold; a deviation between the lever command speed calculated by the lever command speed calculation unit and the actual swing speed detected by the swing speed detection unit is greater than a second threshold; and the lever command speed calculated by the lever command speed calculation unit is smaller than a predetermined value.
 6. An output torque control method for a motor generator performed in a construction machine comprising: an undercarriage; an upper structure swingably provided to the undercarriage and driven by the motor generator; working equipment provided to the upper structure; and a controller, the method comprising steps below performed by the controller of the construction machine: detecting an actual swing speed of the upper structure; calculating a lever command speed based on an operation amount of a swing lever configured to swing the upper structure; calculating a torque command value based on the calculated lever command speed; outputting the torque command value to the motor generator based on the calculated torque command value and the detected actual swing speed of the upper structure; and restricting the output of the torque command value to the motor generator when: the detected actual swing speed is smaller than a first threshold; a deviation between the calculated lever command speed and the detected actual swing speed is greater than a second threshold; and the calculated lever command speed is smaller than a predetermined value. 